The deoxynucleoside, 2-chloro-2'-deoxyadenosine, is known (D. A. Carson, D. Bruce Wasson, and Arnest Beutler, Proc. Soc. Acad. Sci. USA, Vol. 81 pp. 2232-2236, 1984) for its antileukemic and immunosuppressive activity both in primates and in Phase I clinical trial in patients.